Generally, a starch is easily digested. However, the starch also includes an indigestible fraction, and such a fraction is called Resistant Starch (RS).
Non-Patent Document 1 describes that when a feed containing, as a resistant starch, a high-amylose corn starch or heat-moisture treated high-amylose corn starch is given to pigs, bifidobacteria numbers in feces increase.
Moreover, Non-Patent Document 2 describes that when a high-amylose corn starch and probiotic components are mixed with pig's feed, fecal numbers of bifidobacterial increase.
Furthermore, in Non-Patent Document 3, humans ingest the resistant starch so as to investigate changes in the bacteria. It is described that when a group ingests a wheat starch-containing food as a control group, a chemically modified starch of RS type 4 results in a significant difference in the increase in the number of bifidobacteria. On the contrary, it is described that a high-amylose corn starch of RS type 2 does not result in a significant difference in the number of bifidobacteria.